Waste-Heat Exchanger for Sulfur Dew-Point Protection
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Solution Overview
Problem
The challenge of efficiently recovering waste heat for heating burners in paper machines, particularly those used in drying sections, has not been effectively addressed due to the high pollutant loads in combustion waste gases from pulp mills, leading to a lack of integration and control in waste-heat recovery between these units.
Innovation Solution
A method and system for waste-heat recovery that involves combusting secondary fuels and waste materials in a combustion furnace to generate hot combustion waste gas, which is then used to heat a heating burner's combustion supply air through a waste-heat exchanger, maintaining a gas temperature above the dew-point of sulfur compounds to prevent condensation and using plate heat exchangers for efficient heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If waste heat from combustor is used to heat drying section, then energy efficiency is improved, but risk of acid dew-point corrosion increases
Solution Approach 1:
A heat exchanger is introduced as an intermediary device between the combustor waste heat stream and the drying section air stream. This allows thermal energy transfer without direct contact between the corrosive flue gas and the drying air system, thereby recovering waste heat while preventing acid dew-point corrosion in the drying section equipment.
Solution Approach 2:
The harmful components (acidic substances) are effectively removed from the heat transfer process by using the heat exchanger to extract only the thermal energy from the flue gas, leaving the corrosive substances behind in the combustor exhaust stream which is then discharged through the stack.
2Power
If heating output for drying section is increased, then drying performance is improved, but natural gas consumption increases
Solution Approach 1:
The system changes the temperature parameter of the drying air by preheating it with waste heat from the combustor before it enters the drying section. This allows the heating burners to operate at lower fuel consumption while achieving the same drying performance, as the waste heat contributes to the required drying air temperature.
Solution Approach 2:
The system uses its own waste heat output from the combustor to partially supply the heating needs of the drying section, creating a self-service energy loop where the process's own byproduct is utilized to reduce external energy requirements.
3Loss of energy
If waste-heat recovery system is integrated, then energy efficiency is improved, but system complexity increases
Solution Approach 1:
The heat exchanger serves multiple functions simultaneously: it recovers waste heat from the flue gas, preheats the drying air, and acts as a thermal coupling between the combustor and drying section without requiring complex control systems or additional equipment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the need for fossil fuels by transferring thermal energy from the combustion waste gas to the heating burner, saving up to 90% of natural gas usage while maintaining continuous operation and avoiding equipment deposits.
Implementation Method 1
transferring thermal energy from the hot combustion waste gas introduced into a waste-heat recovery device by the at least one waste-heat exchanger to a fluid used as an energy source in the first process unit
Implementation Method 2
combusting of secondary fuels and/or waste materials including sulphur compounds in the combustion furnace of the second process unit to generate hot combustion waste gas
Data Source
AI summary
The invention relates to a method for waste-heat recovery comprising the following steps: providing a first process unit (10), which requires thermal energy, wherein the first process unit (10) comprises a heating burner (15, 16), which is fluidly connected to a fuel supply line (100, 101, 102) and to a combustion-air supply line (112, 113); providing a second process unit (20), in which thermal energy is generated, wherein the second process unit (20) comprises a combustion furnace (21), which is designed to burn waste materials (201) containing sulfur compounds; burning waste materials (201) containing sulfur compounds to generate hot combustion exhaust gas (210) which contains sulfur compounds; discharging the hot combustion exhaust gas (210) from the second process unit (20) and introducing the combustion exhaust gas (310) into a waste-heat recovery device (3) comprising a waste-heat exchanger (31, 32); transferring thermal energy from the combustion waste gas (310) by the waste-heat exchanger (31, 32) to a fluid which is used as an energy source in the first process unit (10), wherein a gas temperature (36, 37) of the combustion exhaust gas (311, 312) downstream of the waste-heat exchanger (31, 32) is set so as not to be below a dew-point temperature of the sulfur compounds in the combustion waste gas (311, 312).